Simulation of Space Charge in LDPE under AC Electric Field

Space charge accumulation is an important issue to be considered in power transmission systems. However, because of the unavoidable limitation of the temporal resolution and spatial of the detection system, the detection is difficult. The numerical simulation of space charge under the AC field can qualitatively explain the source and the charge transportion principle of the space charge under AC field, thus can preliminarily explain the transport process of space charge under the circumstances of the AC field. In this paper, on the basis of the bipolar carrier transport model, the numerical simulation of the space charge transport process in LDPE (Low-density polyethylene) under different frequencies of AC field is carried out. The results show that there is less space charge accumulation in the AC field and accumulation of space charge is mainly concentrated on the surface side of LDPE sample. There is almost no space charge accumulation on LDPE sample surface under the condition that the electric field applied frequency is 50Hz and above. Under the 0.1 Hz electric field, a small amount charge of the same polarity as the electrode appears on the surface side of LDPE sample, there is obvious charge hysteresis at the zero-crossing point of the electric field. When the frequency of electric field are 0.01Hz and 0.005Hz, the amount of accumulated space charge increases significantly, and the hysteresis phenomenon at the zero-crossing point of the electric field becomes more obvious. Only under the low-frequency AC field, there is obvious accumulation of space charge on the surface side of LDPE sample, and the polarity of the charge is the same as that of the electrode field. The above phenomenon may be related to traps inside the medium.